Compared to laboratory adapted viruses, primary isolates of HIV-1 are relatively resistant to neutralization. Conversely, antibodies generated by subunit gp120 vaccines have been largely ineffectual in neutralizing primary isolates. Multiple mechanisms may be deployed by the virus to evade host immune responses. The investigators hypothesize that N-linked glycosylation of the surface antigens of HIV-1 contributes to viral evasion and that selective removal of specific N-linked glycans from HIV-1 surface antigens will result in an increase in the susceptibility of the virus to neutralization and an enhancement of the ability of its envelope glycoproteins to elicit neutralizing antibodies. They propose to test this hypothesis by introducing site-specific mutations in selective N-linked glycosylation sites in the env gene of a primary HIV-1 isolate and to study their effects on the functional and immunogenic properties of the mutant viruses and their envelope proteins. The specific aims of this proposal are: (1) to construct site-specific mutations in the env gene of a primary HIV-1 isolate and to express its envelope glycoproteins lacking specific N-linked glycans; (2) to determine if removal of specific N-linked glycans will alter the functional and antigenic properties of the surface glycoproteins; (3) to re-introduce mutations in N-linked glycosylation sites into the viral genome and to determine the biological and antigenic properties of such mutant viruses, (4) to determine if mutant envelope glycoproteins lacking specific N-linked glycans will have altered immunogenic properties. Results of these studies may enhance understanding of the mechanisms by which the virus evades host immune responses and provide the basis for the development of safe and efficacious vaccines against AIDS.